This invention relates to a variable displacement pump which is employed as a hydraulic source arranged to supply a hydraulic fluid to sliding portions and so on of an internal combustion engine of a vehicle.
A Japanese Patent Application Publication No. 2008-524500 (corresponding to U.S. Patent Application Publication No. 2009/022612 A1, U.S. Patent Application Publication No. 2010/329912 A1, U.S. Patent Application Publication No. 2013/098446 A1, and U.S. Patent Application Publication No. 2013/195705 A1) discloses a variable displacement pump which is a vane type variable displacement oil pump that is used for an internal combustion engine of a vehicle. In this variable displacement oil pump, an eccentric amount of the cam ring is controlled in a two stepped (stepwise) manner by an urging force based on discharge pressures which are introduced into two control hydraulic chambers that are separated between a pump housing and a cam ring, and which are acted in a direction (hereinafter, referred to as concentric direction) in which the eccentric amount of the cam ring with respect to a center of a rotation of a rotor becomes small, and by a spring force of a spring arranged to urge the cam ring in a direction (hereinafter, referred to as an eccentric direction) in which the eccentric amount of the cam ring becomes large. With this, it is possible to supply the oil to a plurality of devices having different necessary discharge pressures.
In particular, when the engine speed is increased, the discharge pressure is introduced into one of the control hydraulic chambers. When the discharge pressure reaches a first predetermined hydraulic pressure which is a first equilibrium pressure, the cam ring is slightly moved in the concentric direction against the spring force of the spring. Then, when the engine speed is further increased, the discharge pressure is also introduced into the other of the control hydraulic chambers, in addition to the one of the control hydraulic chambers. When the discharge pressure reaches a second predetermined hydraulic pressure which is a second equilibrium pressure, the cam ring is further moved in the concentric direction against the spring force of the spring. In this way, the two stepped control is performed.